Field of the Invention
The present invention relates to semiconductor devices and methods of manufacturing the same.
Description of the Background Art
Examples of nonvolatile flash memories include a split gate memory having a floating gate, a control gate, an erase gate and a select gate. Such a nonvolatile flash memory is disclosed, for example, in Japanese Patent Laying-Open No. 2009-44164.
In this publication, after the control gate is patterned, a spacer oxide layer is formed on sidewalls of the control gate. With this spacer oxide layer as a mask, the floating gate below the control gate and the spacer oxide layer is patterned. The spacer oxide layer is then removed.
In the manufacturing method of the above publication, a gate oxide layer below the floating gate is exposed when the floating gate is patterned. Thus, when the spacer oxide layer is removed after the patterning of the floating gate, the exposed gate oxide layer is also simultaneously removed. As a result, the gate oxide layer below the floating gate erodes in a lateral direction, causing a lateral notch to occur in the gate oxide layer. Due to this notch, a stacked structure of the floating gate and the control gate is supported unstably on a semiconductor substrate by the gate oxide layer.
For this reason, if megasonic cleaning (ultrasonic vibration) is applied in this state in order to effectively remove dirt and dust in acid stripping and acid cleaning steps, the stacked structure of the floating gate and the control gate may collapse with respect to the semiconductor substrate.